I can only put this problem down to Virgin Media. I've never ever had slowdowns at OcUK either day or night, so maybe Virgin Media have had more daytime traffic recently or something.
I would put it down to somewhere along with virgin also, probably some part virgin's backbone that gets congested but trace routes show its after it leaves virgin. And starts when it gets to serverstream.net where im guessing OcUK is hosted although any hops after that times out.
1 <1 ms <1 ms <1 ms 192.168.1.1
2 7 ms 7 ms 8 ms bele-cmts-07-lback-20.network.virginmedia.net [81.99.175.1]
3 7 ms 6 ms 7 ms belf-core-1a-ge-200-2264.network.virginmedia.net [213.105.205.73]
4 15 ms 15 ms 15 ms leed-bb-1a-ae3-0.network.virginmedia.net [212.43.163.201]
5 22 ms 20 ms 22 ms 213.152.245.53
6 21 ms 22 ms 43 ms gi1.abv.tcrb.sov.serverstream.net [213.152.245.132]
7 * * * Request timed out.
8 * * * Request timed out.
9 * * * Request timed out.
10 * * * Request timed out.
11 * * * Request timed out.
12 * * * Request timed out.
13 * * * Request timed out.
14 * * * Request timed out.
15 * * * Request timed out.
16 * * * Request timed out.
17 * * * Request timed out.
18 * * * Request timed out.
19 * * * Request timed out.
20 * * * Request timed out.
21 * * * Request timed out.
22 * * * Request timed out.
23 * * * Request timed out.
24 * * * Request timed out.
25 * * * Request timed out.
26 * * * Request timed out.
27 * * * Request timed out.
28 * * * Request timed out.
29 * * * Request timed out.
30 * * * Request timed out.